In recent years, various types of medical analysis have become increasingly decentralized and more accessible to the patient. The testing of bodily fluids represents one example of this decentralization. Many tests that previously had to be performed at a doctor's office and perhaps even analyzed at a separate office can now be performed immediately and inexpensively in the comfort of a patient's home. One example of such a test is blood glucose monitoring, which is widely used among diabetic patients.
Optical analysis has presented itself as one convenient method for analyzing bodily fluids. In a typical optical analysis application, a certain amount of fluid is placed in a read area adapted to allow light to pass through the fluid or to reflect or diffuse upon contact with the fluid. The light as altered by the fluid can then be collected and analyzed, with changes in the light indicating medically significant properties of the fluid. Fluid may be directed to a read area using a “format,” or a platform for collecting and handling the fluid.
A problem arises in that the fluid volumes used for such analyses is very small—typically in the range of from about 50 nl to about 250 nl, though not limited to any given volume. It is preferable to enable testing with a small sample volume, but such a small sample volume calls for the use of a small read area or window upon which the sample is placed and through which light is passed for analysis. Further, the small sample size requires tight tolerances in the manufacture of formats for optical testing. To ensure consistent analysis from sample to sample, it is important to minimize format-to-format variations in the path light travels through an optical format. Any variability in optical path length directly impacts the magnitude of a transmission signal. Smaller sample sizes drive the need for increased consistency in format construction. Solutions to address the problem of optical path length variation between manufactured formats have resulted in costly precision cuvettes, complex molding techniques, or long optical path lengths to minimize the impact of path length tolerance. None of these solutions is ideal for high-production-volume, low cost, and low-sample-volume systems.
One type of format uses a base member with a cover member adhesively connected to the base member. In these formats, the placement of adhesive between the cover and the base is one source of variation in optical path length that tends to reduce the sample-to-sample precision of testing.
There is a need for optical formats that are efficient to manufacture and easy to use, and that result in precise measurements.